Current status of HER2 testing

Abstract

HER2 gene amplification and receptor overexpression by tumors seems to be associated with poorer prognosis and may be predictive of response to certain anticancer therapies. Furthermore, and paramount to the clinician and patient, a positive HER2 status is a prerequisite eligibility requirement for Herceptin (trastuzumab) therapy in women with metastatic breast cancer. As a consequence, issues relating to accurate and reliable laboratory assessment of HER2 status are a matter of significant debate to pathologists and oncologists. Out of a wide range of techniques that have been used in research for the detection of HER2 status, two technologies are now predominant in the routine clinical pathology laboratory: determination of HER2 protein overexpression by immunohistochemistry (IHC) and HER2 gene amplification by fluorescence in-situ hybridization (FISH). This article discusses some of the recent experiences, guidelines, and opinions of pathologists and clinicians concerning aspects of HER2 testing with respect to when to test (at initial diagnosis or pretreatment), the relative advantages/disadvantages of IHC and FISH, and where to test (local or centralized laboratories).